The largest magnetic fields produced by 132 kV cables are where the individual cores are physically furthest apart and when they carry the maximum current.
Underground cables are not constructed to specific designs as overhead lines are so each one is potentially slightly different. Therefore, a hypothetical design that has the cores separated by more than any practical cable would, and which carries a larger load than any practical cable would, has been used to calculate the maximum possible magnetic field. If this hypothetical design is compliant then any practical design, which will produce lower fields, will also be compliant. This hypothetical design could be operated at any voltage, as the magnetic field depends only on the current and the geometry, not on the voltage.
The design chosen has cores separated by 1 metre, buried 1 metre below ground, and carries a load of 1000 A per phase. A graph and table of the magnetic field that this cable would produce are given below.
Table of fields from the same cable.
Magnetic fields |
Distance from centre line |
|
0 m |
5 m |
10 m |
20 m |
30 m |
50 m |
Seperate cores (flat formation) |
1 m spacing
1 m depth
|
72 μT |
12 μT |
3.4 μT |
0.9 μT |
0.4 μT |
0.1 μT |
Magnetic field public exposure limit |
360 μT
|